August 10, 2022, 06:57:01 AM
Forum Rules: Read This Before Posting

### Topic: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary  (Read 7938 times)

0 Members and 1 Guest are viewing this topic.

#### alecia2011

• Very New Member
• Posts: 2
• Mole Snacks: +0/-0
##### Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« on: May 17, 2011, 10:19:50 PM »
A solution is prepared from 12 g NaOH dissolved in enough water to give 500 cm3 of solution; calculate the molarity of the solution.

I have tried so many ways and just get completely stuck.  I don't know where to go anymore or even how to begin this.  pleasee help me solve this.

I've tried:

1.) 12g NaOH * 1cm3/2.13g --> 5.634cm3 NaOH
5.634cm3 NaOH/500cm3 solution --> 1.13% weight
.0113 = 12g NaOH/X --> X=1065g solution
so theres 12g NaOH and 1053g H2O...

I guess I just need help setting up the dang thing, or the steps on how to solve it.
« Last Edit: May 17, 2011, 10:58:36 PM by alecia2011 »

#### enahs

• 16-92-15-68 32-7-53-92-16
• Retired Staff
• Sr. Member
• Posts: 2179
• Mole Snacks: +206/-44
• Gender:
##### Re: Desperate.
« Reply #1 on: May 17, 2011, 10:41:15 PM »
What is the definition of molarity?

#### alecia2011

• Very New Member
• Posts: 2
• Mole Snacks: +0/-0
##### Re: Desperate.
« Reply #2 on: May 17, 2011, 10:46:19 PM »
What is the definition of molarity?

Molarity = mol/L

mol = mass/MW

density of NaOH as 2.13g/cm3

i know cm3 can be interchanged with mL

#### enahs

• 16-92-15-68 32-7-53-92-16
• Retired Staff
• Sr. Member
• Posts: 2179
• Mole Snacks: +206/-44
• Gender:
##### Re: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« Reply #3 on: May 18, 2011, 12:44:19 AM »
So, you know everything.

Density is not needed.

You have 12 g of NaOH, so you have how many mols?
How many liters are in 500 cm3 (as you said, 500mL)?

Again, as you said mols/L. Plug in your mols and your L.

#### AWK

• Retired Staff
• Sr. Member
• Posts: 7982
• Mole Snacks: +555/-93
• Gender:
##### Re: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« Reply #4 on: May 18, 2011, 01:48:41 AM »
Quote
Molarity = mol/L
Just convert mass to moles and put number in numerator, then convert mL to Liters and put this number in denominator - finally divide these numbers
AWK

#### ibrahim_kaream

• New Member
• Posts: 3
• Mole Snacks: +0/-3
##### Re: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« Reply #5 on: November 14, 2011, 03:40:44 PM »
Mt. Wt. of NaOH = 40

you dissolved 12 gm NaOH to 500 ml water (0.5 L)

So,
12 gm ------- 0.5 L
x   gm-------  1 L

x=12/0.5 = 24 gm

So, You prepared a soln. of 24 gm/L

1 M NaOH ----- 40 gm/L
x M NaOH ----- 24 gm/L

X=24/40= 0.6 M

Conclosion: You prepared 0.6 M NaOH by dissolving 12 gm in 500 ml water.

NB: ml = cm3

#### Borek

• Mr. pH
• Deity Member
• Posts: 27142
• Mole Snacks: +1762/-405
• Gender:
• I am known to be occasionally wrong.
##### Re: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« Reply #6 on: November 14, 2011, 06:40:38 PM »
First: giving final answers is against forum rules.

Second: this thread is 6 months old.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### ibrahim_kaream

• New Member
• Posts: 3
• Mole Snacks: +0/-3
##### Re: Desperate --> g NaOH dissolved in H2O to give 500cm3 solution.. calculate molary
« Reply #7 on: November 17, 2011, 03:24:31 PM »
to calculate molarity all you need is just calculate the prepared concentration in the form of gm/Liter, then divide the result by the molecular weight of NaOH.

12 gm/500 cm3=12 gm/500 ml=12 gm/ 0.5 L=24 gm/ L

M=24/40(NaOH molecular weight)=0.6 M